1. Field of the Invention
The present invention relates to a thermodetector for converting temperature into an electrical signal and, more particularly, to a thermodetector incorporating a magnetic field generator such as a permanent magnet and a ferromagnet whose magnetic permeability changes in accordance with a change in temperature to cause a change in magnetic field intensity which is converted to an electric signal.
2. Description of the Prior Art
Generally, a so-called thermodetector has been used for converting a temperature or a temperature change into an electric signal when the temperature is electrically detected for the purpose of displaying the temperature or for use as a signal applied to further apparatus.
Prior art thermodetectors have a temperature sensing element made of a semiconductor or a special ceramic apparatus. Thermocouple type thermodetectors are also known. Thermodetectors having a semiconductor or ceramic temperature sensing element make use of the phenomenon where the electrical resistance of the semiconductor or the ceramic changes in accordance with the change in temperature. A voltage corresponding to the temperature is produced by converting the change in electrical resistance into a change in voltage. In this type of thermodetector, the response of the voltage change to the temperature change is unsatisfactory since the linearity of the voltage change is poor. In addition, the use of a semiconductor or ceramic material as the temperature sensing element causes the thermodetector to be sensitive to vibration and impact.
On the other hand, the thermocouple type temperature detector, which exploits the principle that a thermocouple produces a voltage which corresponds to the temperature, inconveniently requires a cold contact which must be maintained at a constant low temperature. In general, the cold contact is kept in an insulated container containing ice. Thus, either form of thermodetector is impractical since it is either complicated and large in size, or not durable when subjected to vibration and impact.